The present invention relates to a hydropneumatic pressure accumulator comprising a gas chamber, an oil chamber and a metal bellows having an end plate movable in response to volume changes in the gas chamber and oil chamber. A valve releases or shuts off flow of hydraulic fluid from and into the oil chamber, respectively. A valve lifter controls the valve, and can be moved by the end plate into a position closing the valve in the event of movement of the end plate, corresponding to an increase in the volume of the gas chamber, exceeding an assigned maximum value.
In metal bellows accumulators, limitation of the stroke for expansion and contraction of the metal bellows in response to movements of the end plate is known to be necessary to protect the bellows from overloads. In a conventional pressure accumulator of this type (cf. WO 97/46823), for such limitation, the lifter of the valve adjoining the oil chamber is mounted relative to the end plate of the metal bellows in a positional relationship such that the end plate impinges on the valve lifter when a desired end position is reached and displaces the valve when in the shut-off position so that outflow of hydraulic fluid from the oil chamber is prevented when this end position is reached. Consequently, when the valve is closed, a pressure is maintained in the oil chamber of the accumulator which corresponds to the pressure currently prevailing in the gas chamber, even if the connected hydraulic system is to remain without pressure, so that pressure equalization prevails on the metal bellows.
While overloading of the bellows is prevented in the event of absence of pressure from the connected hydraulic system, the danger nevertheless exists of damage to the bellows in the event of states characterized by excess pressure prevailing on the oil side or in the event of absence of prefill pressure on the gas side.
In this case the end plate moves to the point of mechanical impingement on the accumulator housing when the bellows is extended. In the event of such mechanical restriction of the stroke, the bellows is subjected to the action of a pressure difference corresponding to the excess pressure created on one side, which pressure difference may lead to destruction. Consequently, the use of thicker, multilayer metal bellows has been imposed up to this point. As a disadvantageous result, the spring rigidity is greatly increased and the path of the individual turns of the bellows reduced. The use of thicker multilayer metal bellows results not only in greater weight, but also in relatively poor response to changes in pressure.
A generic hydropneumatic accumulator is disclosed in FIG. 4 of PATENT ABSTRACTS OF JAPAN, Vol. 1996, No. 09, Sep. 30, 1996 (1996-09-30) and JP 08 121401 A (NOK), May 14, 1996 (1996-05-14), with a gas chamber, an oil chamber and a metal bellows separating these chambers. The metal bellows has an end plate movable in response to volume changes from the gas chamber to the oil chamber. Inside the housing enclosing the metal bellows, the housing is penetrated by a separating plate with a fluid connection. The fluid connection carrying fluid delimits the inside of the metal bellows with the inside of an additional fluid chamber within the housing. The additional fluid chamber in that location is connected externally by a hydraulic connection carrying fluid on the bottom side of the housing with sections of a hydraulic circulation system. A valve lifter connected with the end plate of the metal bellow has a closing element. Both sides of the closing element facing each other are in the form of a valve cone and capable of being brought into contact firstly with a valve seat positioned on the separating plate, and secondly, with a valve seat in the hydraulic connection on the bottom side pointing in the direction of the inside of the additional fluid chamber. The apexes of the tapered surfaces of the valve cones and the valve seats both face away from each other, with the tapered surfaces yielding good sealing behavior. Due to the additional fluid chamber, this conventional device builds up pressure on a large scale and in response to fluid volume to be moved in the metal bellows. In the additional fluid chamber, the control behavior of the valve is inhibited so that at least short-term overloads of the metal bellows can occur.
Objects of the present invention are to provide a pressure accumulator having oil and gas chambers separated by a metal bellows in which overloads of the metal bellows during operation can be prevented.
In a hydropneumatic pressure accumulator of the present invention, these objects are attained by the hydraulic connection containing a valve with two valve seats. The apexes of the tapered surfaces of both valve seats and both valve cones face each other. The valve seats are positioned axially between the valve cones. As a result, a compactly designed hydro accumulator is devised. Also, actuation of the valve in the hydraulic connection is accorded directly by the end plate of the metal bellows. Based on the low fluid volume to be controlled in the metal bellows, even in addition to a reduction of weight in contrast to the conventional solutions, especially good response behavior results. Furthermore, overloads of the metal bellows are prevented.
When, in operation of the pressure accumulator of the present invention, pressure equalization has been established between gas prefill pressure in the gas chamber and hydraulic pressure in the oil chamber and the end plate of the metal bellows is between the end positions assigned to it with the oil valve open, this operating condition of equalization of pressure on the bellows is maintained, no matter how sharply the hydraulic pressure of the oil side may drop relative to the gas prefill pressure. When the desired end position is reached, the valve closes and flow from the oil chamber is prevented. No matter how sharply the hydraulic pressure may rise relative to the gas prefill pressure, the valve is closed when the pertinent end position of the end plate is reached, so that flow into the oil chamber is no longer possible.